It may perhaps be said:--"The traces of prochronism you have adduced in created organisms may be granted, because they are inseparable from the presumed condition of those organisms respectively. The blood in the vessels, the hair, the teeth, the nails, may afford evidences of past processes; but then those are only past stages of what yet exists. The case, however, is not parallel with the fossil skeletons, many of which have no connexion with anything now existing. The concentric rings of a timber-tree are essential to its adult state; but how is the existence of the _Pterodactyle_ or the _Megatherium_ essential to that of the recent _Draco volans_, or the South American Sloth? Can you show in the new-formed creature any trace of some organ which does not come into its present condition of being,--of something which has quite passed away?" Perhaps I can. The very concentric rings of the tree are considered by botanists as, in some sense, dead. The paradoxical dictum of Schleiden,--"No tree has leaves,"[108]--is grounded on this circumstance, that the woody portion of the mass is the inert result of former generations, and that the present race of leaves is growing, not out of the woody portion of the tree, but out of its herbaceous extremities, "which grow upon the woody stem _as upon a ground_, formed by the process of vegetation. This common ground, namely, the woody stem, _which is almost lifeless_ in comparison with the herbaceous parts engaged in active growth, is annually covered with a vigorous sheath under the protecting bark; and this sheath is the ground of the nourishment of all the vegetating herbaceous extremities."[109] The polygonal plates into which the bark of the _Testudinaria_ divides, not only show many superposed laminae, at any given moment of its adult condition, but also bear witness, in the broad existent surface of each one, to former laminae, yet older than the oldest now present, which have disintegrated and dropped off. The Palm and the Tree-fern show, in their trunk-scars, evidences of organs which have completely died away and disappeared; while, between these scars and the generation of living fronds, there is, at any given moment of the tree's history, a series of fronds which are quite dead and dry, but which have not yet disappeared. The _Nerita_, a genus of beautiful shells from the tropical seas, dissolves away and removes, in the progress of growth, the spiral column, which originally formed the axis of development; so that, in adult age, the spiral direction of the whole testifies to the past existence of a column which has quite disappeared.